1. Technical Field
The present invention relates to an X-ray diagnostics apparatus, and it particularly relates to a technique for processing a synthesized image area obtained by a television camera unit that utilizes a CCD (charge coupled device) image plate.
2. Background Art
In the X-ray diagnostics apparatus, X-rays are irradiated to an object such as a human body, and an X-ray image permeated through the object is converted to an optical image. The optical image is converted to a television image signal which is then displayed on a picture plane of a monitor as a fluoroscopic image. The fluoroscopic image displayed on the monitor is utilized for diagnosis of a medical patient.
In other words, the X-ray diagnostics apparatus basically consists of:
an X-ray tube for irradiating the X-rays toward the object;
an image intensifier (hereinafter simply referred to as I. I.) for converting the body-permeated X-ray image to the optical image;
a television camera unit for converting the optical image outputted from the I.I, to the television image signal; and
a monitor which displays the television image signal output from the television camera as the fluoroscopic image.
The television camera recently in use utilizes generally a fixed charge-coupled-device (CCD) image plate where the optical image is converted to the television image signal by means of photosensitive conversion.
Since there is limit for the number of pixels available for a single image plate, there is caused a problem where resolution degree for the image obtained by the single image plate for the television camera is not sufficient in order to see the image properly. In view of such a problem and in order to improve the resolution degree for the image, there is used a television camera equipped with two image plates 1, 2, lenses 11a, 11b, 11c and half mirror 12, as shown in FIG. 1.
Referring to FIG. 1, the optical image output from I.I 10 is formed in a lower-end portion of image plate 1 through lens 11a, half mirror 12 and lens 11b. Simultaneously, the optical image output from I.I 10 is also formed in a left-end portion of image plate 2 through lens 11a, half mirror 12 and lens 11c.
With reference to FIG. 2, when image plates 1, 2 are overlapped in a manner illustrated in FIG. 2, a single image is constituted by two image plates. Thereby, the resolution power therefor is improved as approximately twice as precise, compared to that obtained by using only single image plate.
However, there is caused a following problem even in utilizing two image plates. A distribution factor is not equal between lens 11b and lens 11c whose respective arriving rays are reached thereto through half mirror 12. Besides, sensitivity for CCD per se differs between respective image plates 1, 2.
In view of the above drawbacks and in order to equalize outputs from respective plates 1, 2, the same applicant offers a television camera in which average values output from image plates 1, 2 are made equal, in Japanese Patent Laid Open Helsel-3-13078 (filed on 9 Jun., 1993).
In the Japanese Patent Application 3-13078, a method is disclosed by which each average value for output of each image plate is made equal between image plates 1, 2. In other words, the average image density for two image plates is made equal in an area which is overlapped by both two image plates 1, 2. However, there is a drawback in the Japanese Patent Application 3-13078. That is, a density change (so-called shading) due to local sensitivity deviation for respective image plates 1, 2 cannot be corrected.
Namely, even if the averaged values for the outputs from respective image plates 1, 2 are equal, sensitivity distribution for each location at image plates 1, 2 are not even in general. FIG. 3 illustrates such an uneven sensitivity distribution where a vertical line indicates the sensitivity and a horizontal line corresponds to position and location of the image plates substantially taken along lines A-A' shown in FIG. 2. In FIG. 3, a solid curve specified by CCD1 shows the sensitivity of image plate 1, whereas a broken curve CCD2 the sensitivity of image plate 2.
Referring to a graph shown in FIG. 3, image plate 2 is brighter than image plate 1 in a left-half side of the image, while image plate 1 is brighter than image plate 1 in a right-half side of the image. As a result thereof, uniformity of the image as a whole is lost, thus giving an viewer somehow a feeling of physical disorder.